1. Field of the Invention
The present invention relates to epoxy amine adducts having substantial side chain branching, processes for making them and to binders that employ these adducts. The binders are environmentally safe, have a low solvent content and can be used in pigmented and unpigmented systems.
2. Description of Related Art
To protect the environment, it has been an objective to reduce the emission of organic compounds, especially the amount of solvent. The solvent content of adhesives, sealing compounds and coating materials must be reduced in the future from the values which are still customary today, on the basis of statutory regulations (e.g. VOC (Volatile Organic Compounds) regulations in the USA and Great Britain and "TA Luft" German air pollution control regulations! in Germany).
This country-specific statutory pressure is exerted with varying degrees of severity in different countries. The statutory authority permits different evaluations (individual considerations, combined considerations), which impel the producer of such coating, adhesive and/or sealing products to provide new and different levels of technical performance. This has reached the extent where the usually high performance level of such products must on environmental grounds be cut back to a minimum level.
Clearcoats as unpigmented systems are employed in automotive refinishing, for example, as the topmost coat. Their function typically is to protect the pigmented, lower coat (basecoat) against mechanical stress, against the effect of weathering and against dirt, and to provide the overall coating system with the necessary gloss. These clearcoats predominantly have been formulated with polymeric binders which have usually been employed simultaneously in pigmented topcoats as well. The severe VOC regulations, however, force the producer of raw materials to formulate this clearcoat separately, in some cases, with the addition of low molar mass polyols, as a "blend system" (EP-A-0 588 314, EP-A-0 129 124 and U.S. Pat. No. 5,098,956).
Various methods can be used to reduce the solvent content. For example, polymeric binders of extremely low molar mass are used, alone or in blends with binder components of higher molar mass. Highly complex binder systems are known, for example, which comprise mixtures of oligomeric caprolactone polyols, i.e. polyester polyols with acrylate polyols and/or acrylate star polymers (WO 92/22618). Certain organic compounds, for example, aspartic acid derivatives, aldimines, ketimines or oxazolidines (EP-A-0 470 461, EP-A-0 403 921, U.S. Pat. No. 5,214,086, and Robinson et al., "High performance polyurethane coatings systems utilizing oxazolidine based reactive diluents" 21st Higher Solids and Waterborne Coatings Symposium (February 1994) New Orleans, La., USA) also are described as reactive diluent systems or as sole binders.
The maximum amount of volatile organic constituents that are permitted for the clearcoat in automotive refinishing in California, for example, is 3.5 lb/gal (0.42 kg/dm.sup.3), i.e. a mass fraction of solids of about 59% in the coating material (DIN 53 211, 4 mm cup, 21 s flow time at 23.degree. C.). The restrictions become more severe when a conventional basecoat is applied: the overlying clearcoat must not exceed a VOC limit of 2.1 lb/gal (0.25 kg/dm.sup.3, i.e. a mass fraction of solids of about 75% ). Important processing properties then are lost when extremely low molar mass polyols are used, for example, the rapid drying of the clearcoat. When the above-mentioned organic compounds are employed, there is no guarantee of a long pot life (processing time). In addition, partial dissolution of the basecoat or skinning, in some cases cloudiness, and gas-escape defects are observed with the rapid reactive diluent systems. The original aim of enabling the use of these binders in pigmented systems as well as unpigmented systems, however, cannot be achieved in this case.
Thus, there exists a need to develop environmentally friendly binder systems having a low solvent content which give rise to rapid drying, a long pot life, little or no partial dissolution of the basecoat, and no skinning, cloudiness or gas-escape defects. There also exists a need to provide binder systems that are universally useful in unpigmented and pigmented systems. Moreover, there exists a need to be able to use these systems in environmentally friendly adhesives and sealing compounds.